The present invention pertains to tension loss indicators for a wheel lug nut. More particularly, the present invention pertains to devices for indicating a loss of torque in a lug nut, such as that used for mounting wheels for trucks and utility vehicles.
One type of lug nut is a PACNUT(copyright) (PACNUT(copyright) is a registered trademark of Illinois Tool Works of Glenview, Ill.). The PACNUT(copyright) includes a stack of conical washers assembled on a base washer. The conical and base washers are held in place by a cage and are internally threaded to secure to, for example, a threaded bolt shank. When the PACNUT(copyright) is placed in tension, the conical washers are flattened to produce a locking action that results in tension or stretch in the joint. Exemplary of a PACNUT(copyright) type of fastener is that fastener disclosed in Mitts, U.S. Pat. No. 6,015,253 and Reynolds, U.S. Pat. No. 4,900,209.
These fasteners are used in wheel lug nut applications, typically for trucks and other large utility vehicles. Use of these fasteners facilitates proper tensioning of the wheel to hub joint. Such applications, however, present several critical challenges. For example, it is critical that tension on a stud secured with this type of fastener is carefully monitored for safety reasons. Proper torque on the fastener or tension in the joint provides one indication of safe operating conditions.
One known method for measuring the tension on the stud is to measure the torque applied to the fastener such as with a torque wrench. This, however, is a labor intensive undertaking and requires specialized, calibrated tools for measuring the torque. This is particularly the case for large semi-tractor trailers and the like which may include as many as ten fasteners per wheel and more than sixteen wheels for tandem truck arrangements.
Also known are caps that include indicating arrows to indicate that the nut has not moved. Such an indicating cap is disclosed in Patti, U.S. Pat. No. 5,120,174. In such a cap, indicia, such as arrows, are oriented in a particular direction (e.g., aligned with one another) to indicate that the nut has not moved and therefore that tension in the joint is acceptable. A change in the arrow orientation generally indicates that the tension has changed and that a failure may have occurred. However, indicating caps require close visual inspection in order to make a determination of whether the arrow orientation has changed from a predetermined setting. In addition, it is possible that the tension in the joint can decrease to an unacceptable or unsafe level without the nut moving.
Accordingly, there exists a need for a utility hub lug nut tension or torque loss indicating device that provides ready indication of a change in tension in the joint (or tension on the fastener). Desirably, such a device is self-indicating, and is used without requiring the application of torque to the fastener. Most desirably, such a device is inserted or positioned over the fastener to provide such tension-loss indication quickly and accurately.
A tension loss indicator for use with a fastener provides readily discernible visual indication of improper tension in the joint or loss of tension in the joint. The fastener is formed from a stack of conical washers confined in the stack by a cage. The stack defines an uppermost washer having an upper surface and further defines an interior region intermediate an edge thereof and a longitudinal axis of the stack. The cage includes longitudinally extending side portions having a slot formed therein.
In one embodiment, the indicator is configured as a cap that cooperates with and is positioned over the fastener. The cap includes a body configured for receipt over the fastener conical washers. The body defines an interior surface. A base flange is contiguous with the body.
At least one stanchion, and preferably a plurality of stanchions extend inwardly of the cap from the interior surface. Each stanchion defines an end longitudinally spaced from the base flange. The cap further includes at least one, detent and preferably a plurality of detents, each extending inwardly of the cap from the interior surface. The detents are longitudinally spaced from the base flange. The detents can be circumferentially spaced from the stanchions.
When the stack of conical washers is placed under tension with the uppermost washer in a planar condition, the stanchions lie adjacent the uppermost washer at the interior region and the detents engage and secures into the slots in the cage side. This secures the cap to the fastener. Conversely, when the stack of conical washers is under a tension that is insufficient to urge the uppermost washer into the planar condition, the stanchions abut the uppermost washer at the interior region and the detents are disengaged from the slots in the cage. This prevents the cap from securing to the fastener cage and/or dislodges the cap from the fastener.
In a current embodiment, the interior surface of the cap body defines a hexagonal cross-sectional shape, defining six contiguous side surfaces. In this hexagonal arrangement, the cap preferably includes three stanchions extending inwardly of the cap from alternating ones of the six contiguous sides, and three detents extending inwardly of cap from alternating others of the six contiguous sides. The cap body is preferably enclosed. The base flange can extend radially outwardly of the body.
An alternate embodiment of the tension loss indicator includes a body defining a central nut bore that is configured to snuggly receiving the fastener. A through body eccentric bore is contiguous with and opens into the nut bore.
At least one, and preferably a plurality of stops are disposed within the central nut bore. The stops define a baseline plane relative to an outermost periphery of the uppermost washer when the fastener is positioned within the nut bore, in contact with the stops.
The indicator includes indicating means, such as a mechanical displacement gauge that is positioned within the eccentric bore for determining a height of the uppermost washer at a location intermediate the outer periphery of the uppermost washer and the longitudinal axis of the stack. The height of uppermost washer (flexed or unflexed) is determined relative to the baseline plane at the outer periphery of the uppermost washer.
In a preferred embodiment, the gauge includes a stem portion having a tip, and the eccentric bore is positioned such that the stem tip contacts the fastener immediately adjacent a central stud-receiving opening. In a most preferred embodiment, the fastener stops are formed integral with the body.
These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims.